The world’s two largest iron-ore exporters Brazil and Australia will each add about 100 million metric tons of supply through the end of the decade, boosting a global glut and hurting prices in a slump that will then force marginal miners to cut output, according to Citigroup Inc.

Shipments from Brazil will expand to 480 million tons in 2020 from 371 million this year, while Australian cargoes rise to 934 million tons from 835 million, the bank said in a report. That’ll lift the surplus to 56 million tons in 2018 from 20 million this year, before price-induced curtailments help bring the global market back toward a balance, Citigroup estimates.

While iron ore has rallied in 2016, confounding predictions for renewed losses, investors are now refocusing on prospects for rising output from the top suppliers. With Brazil’s Vale SA set to start a four-year ramp-up of its S11D project, banks from Morgan Stanley to Citigroup as well as BHP Billiton Ltd. have said the additional output will probably contribute to weaker prices.

‘Strong Headwinds’

The expansion of ore supply is on track, with restarted capacity a swing factor, Citigroup analysts including Ed Morse wrote in the report received on Monday. “We expect iron ore prices to find some support in the next one to two months, but should face strong headwinds thereafter through 2017.”

The raw material with 62 percent content delivered to Qingdao was little changed at $56.77 a dry ton on Monday, according to Metal Bulletin Ltd. Prices are 3.7 percent lower in September, heading for their first back-to-back monthly decline since November 2015. Citigroup reiterated its outlook for ore dropping to $45 next year and $38 in 2018.

The global surplus will probably start to shrink after 2018, dropping from 56 million that year to just 8 million tons in 2019, the bank forecast. It estimated price-induced curtailments would be about 150 million tons in 2018 and more than twice that figure in 2020.

Prices may soften toward year-end as supply increases, Virginia Wilson, BHP’s general manager of iron ore marketing, said at a conference last week. Among new projects is Vale’s S11D, which will have the capacity to produce 90 million tons a year. Inaugural cargoes are expected in January, Vale’s executive manager for shipping and iron ore marketing Luiz Meriz told the gathering.

SGX AsiaClear futures point to lower prices, with the contract for October trading at $55.67 a ton, January’s at $50.60 and next September’s below $45. Miners’ shares were mixed in Sydney on Monday, with BHP closing 0.1 percent higher, Rio Tinto Group rising 0.6 percent and Fortescue Metals Group Ltd. lower. The trio are Australia’s top shippers.